It is often desirable or necessary to assay for the presence of bacteria or other microorganisms in various clinical, food, environmental, or other samples, in order to determine the identity and/or the quantity of the microorganisms present. Bacterial DNA or bacterial RNA, for example, can be assayed to assess the presence or absence of a particular bacterial species even in the presence of other bacterial species. The ability to detect the presence of a particular bacterium, however, depends, at least in part, on the concentration of the bacterium in the sample being analyzed. Concentration of the bacteria in the sample can shorten the culturing time or even eliminate the need for a culturing step. Thus, methods have been developed to isolate (and thereby concentrate) particular bacterial strains by using antibodies specific to the strain (for example, in the form of antibody-coated magnetic or non-magnetic particles). Such methods, however, have tended to be expensive and still somewhat slower than desired for at least some diagnostic applications. Non-specific concentration or capture of microorganisms has been achieved through methods based upon carbohydrate and lectin protein interactions. Various inorganic materials (for example, hydroxyapatite and metal hydroxides) have also been used to non-specifically bind and concentrate bacteria. Such non-specific concentration methods have varied in speed, cost, sample requirements, space requirements, ease of use, suitability for on-site use, and/or effectiveness.
Rapid methods based on ATP bioluminescence assays have been used to determine microbial contamination in water as they provide immediate results; however, the methods are limited by detection sensitivity because they require at least 1×105 colony forming units (cfu)/ml to elicit detectable responses. One can increase the sensitivity of the ATP bioluminescence assay by using a larger volume of sample (e.g., 100 ml), but such methods can be difficult to implement in the field.